Chelsea will resist demands from the referees' union for an unreserved apology and financial compensation for Mark Clattenburg after he was cleared of directing a racist comment at Mikel John Obi.

The Premier League referee spoke of his huge relief after the Football Association found he had no case to answer, describing the "frightening" allegations as the most stressful experience of his life. But Chelsea will resist calls for a direct apology, believing they acted in good faith at all times and had a duty to support Ramires. The Brazilian claimed he heard the referee say "shut up you monkey" to Mikel in the wake of the sending off of Fernando Torres during Chelsea's home defeat to Manchester United on 28 October.

"We are seeking a full and unreserved apology and compensation for loss of earnings, damage to reputation and stress. We are also asking for a sizeable donation to Show Racism the Red Card and Kick it Out," said Alan Leighton of Prospect, the referees' union. "The charge was based on the flimsiest evidence that should never have got to this stage. It should never have been made public and should have been dealt with confidentially."

In an effort to avoid any ambiguity in future, all conversations between referees and with players will now be recorded. The new equipment will be brought in "as soon as possible" and should be in use within a fortnight, according to Mike Riley, general manager of PGMOL, the referees' body. Asked whether the club should apologise, Riley said: "I hope Chelsea will do the right thing."

An hour before Chelsea prepared to unveil Rafael Benítez as their new interim manager following a tumultuous week, the club was informed by the FA that Clattenburg did not have a case to answer.

Coming in the wake of the John Terry case that hung over Chelsea for 12 months and prompted criticism when he remained as club captain despite being found guilty of racially abusing QPR's Anton Ferdinand, the case added to the already febrile atmosphere at Stamford Bridge even before this week's sacking of Roberto Di Matteo. Chelsea immediately came under fire for not apologising directly to Clattenburg, who had been accused of using "inappropriate language".

Ramires continues to insist that he heard the offending term. While accepting the verdict, the club said they were right to back their player and merely said they hoped "all concerned can continue to carry out their duties without prejudice".

Benítez said he had not had time to form a view, having flown in on Thursday morning and met the squad for the first time in the afternoon. "I just arrived and went straight to the training session. I didn't have time to think about other issues, just to think about the things I want to do," he said.

Mikel was charged by the FA with using threatening or abusive words and/or behaviour "in or around the Match Officials' changing room" following the fractious 3-2 home defeat to United, during which Torres and Branislav Ivanovic were sent off. He has until Friday 30 November to respond.

Clattenburg, who has been omitted from the refereeing list for four weeks, paid tribute to the support of his colleagues and said he "couldn't wait" to get back to officiating.

"The messages of encouragement from those inside and outside of the game have helped me through the most stressful time of my professional life. To know you were innocent of something but that there was the opportunity for it to wreck your career was truly frightening," he said.

The FA's investigators found that neither Clattenburg nor the three other match officials – who could hear everything being said in their earpieces – heard the comment. Nor did Mikel, who was much closer to the referee than Ramires, hear what it is suggested was said to him. It was only after the match that Ramires was able to explain fully the allegation, prompting Mikel to furiously confront the referee. Nor was there anything in the video evidence to support the allegation and nor did two other players near the incident, one of whom was Ashley Cole, hear anything untoward.

"Having considered all of the available evidence it was the opinion of David Waters QC, independent counsel, that the evidence of Ramires was not supported by any other evidence. Moreover it was contradicted by other witnesses and does not cross the evidential threshold required to bring a charge against Mark Clattenburg," the FA said.

Riley said: "It is PGMOL's considered view that Mark is completely exonerated of the allegation and he will return to active duty shortly without any stain on his character or reputation. The verbal and visual facts do not support any of the allegations made against him. They make it clear that Mark did not use any inappropriate language towards any Chelsea player."

It is understood that neither Clattenburg nor his colleagues recall him using any language that could have been misheard by Ramires as "monkey". However, the FA underlined that it believed the Brazilian had acted in good faith.

Chelsea, under intense pressure following criticism of their handling of the fallout from the Terry case, said they accepted the FA's verdict but defended their decision to pursue the complaint.